1. Field of the Invention
This invention broadly relates to an appliance used in orthodontic treatment. More particularly, the present invention relates to an orthodontic appliance such as a bracket or buccal tube having a releasable latch for releasably retaining an archwire in an archwire slot of the appliance.
2. Description of the Related Art
Orthodontic therapy is a specialized type of treatment within the field of dentistry, and involves movement of malpositioned teeth to orthodontically correct locations. Orthodontic treatment often improves the patient""s occlusion and typically enhances the aesthetic appearance of the teeth.
Many types of orthodontic treatment programs involve the use of a set of tiny appliances and wires that are commonly known collectively as xe2x80x9cbracesxe2x80x9d. During such treatment programs, small appliances known as brackets are fixed to the patient""s anterior, cuspid and bicuspid teeth, and an archwire is inserted into a slot of each bracket. The archwire forms a track to guide movement of the teeth to orthodontically correct locations. End sections of the archwires are typically captured in tiny appliances known as buccal tubes that are fixed to the patient""s molar teeth.
Many types of orthodontic brackets have archwire slots that are open on one side for insertion of the archwire, and bounded on remaining sides by walls or other structure. Brackets that are intended to be bonded to the patient""s front tooth surfaces often have archwire slots that are open either on a buccolabial side (i.e., a side facing the patient""s cheeks or lips) or an occlusal side (i.e., a side facing the outer tips of the teeth) of the archwire slot. Some brackets, however, are intended to be fixed to the lingual side of the patient""s teeth (i.e., the side of the teeth facing the patient""s tongue) and in that instance typically have an archwire slot that is open on a lingual side or on an occlusal side.
Many orthodontists use ligatures to connect the archwire to the brackets and to urge the archwire into an orientation of seating engagement in the archwire slot. One type of commercially available orthodontic ligature is a small, elastomeric O-ring. Orthodontic O-rings are installed by stretching the O-ring around small wings (known as xe2x80x9ctiewingsxe2x80x9d) that are connected to the bracket body on the gingival side (i.e., the side facing the patient""s gingiva or gums) and on the occlusal side of the archwire slot. Once installed, the O-ring ligature extends around the tiewings as well as over the labial side of the archwire and urges the archwire toward a fully seated position in contact with a lingual wall of the archwire slot.
Metal ligatures, such as ligatures made of stainless steel, are also used to retain archwires in archwire slots of brackets. Metal ligatures are typically made of a short section of initially straight wire. During installation, the wire ligature is hooked around the tiewings and extended over the labial side of the archwire. End sections of the ligature are then twisted together to form a loop to retain the ligature in place.
Unfortunately, some orthodontists are not entirely satisfied with elastomeric and metal ligatures. Such ligatures are somewhat time-consuming to install, both during initial installation and also during reinstallation whenever replacement of the archwire or ligatures is desired. As can be appreciated, a savings in the amount of time needed for ligation can help to reduce the total time that the practitioner must spend with the patient and consequently aid in reducing the overall costs of orthodontic treatment.
Other disadvantages are also associated with elastomeric and metal ligatures. For example, there have been reports that certain polyurethane elastomeric ligatures have exhibited deformation and force decay during the course of treatment. In some instances, elastomeric ligatures are stained by food and beverages consumed by the patient and become somewhat unsightly. Metal ligatures often have sharp ends that may retain plaque and food debris and also may increase the risk of infection.
In an effort to overcome the problems associated with conventional ligatures, a variety of orthodontic brackets have been proposed having various types of latches for coupling the archwire to the bracket. Such brackets are also known as self-ligating brackets. The latch comprises a clip, spring member, cover, shutter, bail or other structure that is connected to the bracket body for retaining an archwire in the archwire slot.
Examples of self-ligating orthodontic brackets having generally U-shaped ligating latch clips are described in U.S. Pat. Nos. 3,772,787, 4,248,588 and 4,492,573. In general, the clip of such brackets is slidably mounted on the bracket body, and a dental explorer or other small-tipped dental tool is used to move the clip relative to the body when needed in order to open or close the archwire slot. A self-ligating bracket known as the xe2x80x9cSpeedxe2x80x9d brand bracket also has a movable, generally U-shaped clip for ligating the archwire to the bracket.
Other types of self-ligating brackets have latches that resemble swinging shutters or closures that pivotally move between a slot-open and a slot-closed position. For example, U.S. Pat. No. 4,712,999 has a rotatable cover plate that is pivotally connected at one end to a tiewing of the bracket along one side of the slot, and is releasably engagable at the other end with a tiewing that is located along the opposite side of the archwire slot. Other orthodontic brackets with swinging latches are described in U.S. Pat. Nos. 4,103,423, 5,516,284 and 5,685,711.
U.S. Pat. Nos. 4,371,337 and 4,559,012 describe self-ligating orthodontic brackets having latches that rotate about the longitudinal axis of the archwire slot. The latch of these references has a somewhat cylindrical shape and is rotatably received in a mating, cylindrical channel, and an outwardly extending arm is provided to assist in rotatably moving the latch between a slot-open and a slot-closed position.
A self-ligating orthodontic bracket that is described in U.S. Pat. No. 5,711,666 has a latch that comprises a flexible flat spring member. One end of the spring member is fixed to the bracket body on one side of the archwire slot, and the opposite end of the spring member has notches that releasably engage latch sears or catches when the spring member is moved to a slot-closed position. To open the slot, the notches are disengaged from the catches and the spring member is bent to an orientation sufficient to enable the archwire to be removed from the archwire slot.
Other types of self-ligating orthodontic brackets have latches that comprise essentially flat plates that are slidable between a slot-open and a slot-closed position. Examples of such construction are shown in U.S. Pat. Nos. 5,094,614, 5,322,435 and 5,613,850. In general, the sliding latches described in those references move in upright channels that are located buccolabially of the archwire slot.
Another type of self-ligating bracket that has been proposed in the past has a latch that is made of a section of wire material that functions similar to a bail. The orthodontic brackets described in U.S. Pat. Nos. 4,149,314, 4,725,229 and 5,269,681 have wire-like latches that swing between a slot-closed position and a slot-open position. The orthodontic bracket described in U.S. Pat. No. 4,260,375 has a wire latch that is slidable between a slot-open and a slot-closed position.
Many practitioners prefer self-ligating orthodontic brackets over brackets that are not self-ligating because the need to ligate each bracket with an initially separate elastomeric O-ring or a metal ligature wire can be avoided. However, conventional self-ligating orthodontic brackets are not entirely satisfactory because of the lack of optimal control over movement of the underlying teeth. During the course of treatment, it may be necessary to shift each tooth relative to adjacent teeth in order to provide an aesthetically pleasing result at the conclusion of treatment. Precise control over movement of the teeth is desirable so that each tooth can be shifted as needed to its exact, intended orientation and in proper orthodontic relation relative to other teeth in the oral cavity.
In general, there are three types of tooth movement that are important to orthodontic practitioners. Tipping movement is one such type of movement, and may be defined as pivotal movement of the long axis of a tooth in a mesial-distal direction. Another movement is torque movement, and can be defined as pivotal movement of the long axis of a tooth in a buccal-lingual direction. The third type of tooth movement is rotational movement, and can be defined as rotational movement of a tooth about its long axis. Preferably, the appliances selected by the practitioner for use provide precise control over movement of the associated teeth for each type of tooth movement.
One problem that has been noted in connection with conventional direct-bonded appliances, including self-ligating brackets, is the possibility that such brackets may spontaneously debond from the patient""s tooth when the teeth are severely maloccluded. For example, if one of the patient""s teeth is located a relatively large distance in a lingual direction relative to adjacent teeth in the dental arch, the archwire must be deformed a significant distance in order to engage the archwire slot of the bracket. In such instances, the inherent tendency of the archwire to return to its normally arch-shaped configuration will cause the archwire to exert a substantial force on the appliance bonded to the severely maloccluded tooth. Unfortunately, the bracket may then debond from the tooth if the archwire exerts a force that is larger than the force required to debond the bracket in the same direction.
Brackets that spontaneously debond from teeth represent a waste of time and expense for both the practitioner and the patient, and are best avoided if at all possible. Once a bracket has unintentionally debonded from a tooth, the archwire is removed from the slot of each bracket and the tooth is cleaned and etched in preparation to receive another bracket. If the debonding occurs outside of the practitioner""s office, the orthodontic treatment of that tooth is interrupted until such time as the patient returns to the practitioner""s office for replacement of the bracket.
In the past, practitioners have sometimes used relatively small-diameter archwires in the initial stages of orthodontic treatment when one or more teeth in the dental arch are severely maloccluded. Such archwires provide relatively little force to the appliances, and as a consequence reduce the likelihood that appliances that are directly bonded to severely maloccluded teeth will spontaneously debond during the course of treatment. Unfortunately, the use of such small-diameter archwires somewhat retards the progress of treatment in comparison to the use of larger diameter archwires, since the force provided by the archwire to all of the teeth is somewhat reduced.
While many types of self-ligating orthodontic appliances have been proposed in the past, there remains a continuing need to improve the state of the art so that the treatment program can be completed in prompt fashion, the duration of the patient""s appointments can be shortened and the practitioner""s efficiency is increased. For example, it would be desirable to provide a self-ligating appliance that reduces the time needed for installation of an archwire in comparison to conventional self-ligating brackets, so that the time of both the practitioner as well as the patient to complete the installation procedure can be reduced. Moreover, it would be desirable if such an appliance could provide precise control over movement of the associated tooth while also facilitating movement of the tooth to its desired ultimate location.
The present invention is directed toward an orthodontic appliance such as a bracket or buccal tube having features that represent significant advantages over known self-ligating appliances. In one aspect of the invention, the appliance has a latch for releasably retaining an archwire in the archwire slot. The latch releases the archwire from the archwire slot whenever the archwire exerts a force on the appliance that exceeds a certain minimum value. The minimum value is significantly less than the force required in the same direction to debond the appliance from the tooth, and consequently helps ensure that the appliance will not spontaneously debond from the tooth during the course of treatment.
The self-releasing latch of the present invention is also beneficial in that the maximum force exerted by the appliance on the patient""s tooth can be limited to a pre-selected value, which in some instances may be lower than the force required to debond the appliance from the tooth. As a result, the amount of any pain experienced by the patient due to forces exerted by the appliance is also limited. The force limiting latch also helps ensure that undue force is not exerted on root portions of the associated tooth so that blood vessels adjacent the root portions are not significantly compressed and blood in the vessels continues to freely circulate to facilitate bone regeneration.
Another aspect of the invention is directed toward a self-ligating appliance having a latch that is movable to a slot-open position to enable passage of an archwire into the slot by pressing the archwire against the latch in a lingual direction. The occlusal side and the gingival side of the archwire slot are immovable relative to each other, and thereby provide good control over movement of the appliance and the associated tooth whenever torquing, tipping, intruding or extruding of the tooth is desired.
Other aspects of the invention relate to a self-ligating orthodontic appliance having a latch that comprises at least one clip. The clip provides certain advantages when manufacturing the appliance, and also enhances the practitioner""s control over movement of the associated teeth.
In more detail, the present invention is directed in one embodiment toward an orthodontic appliance that comprises a base for bonding an appliance to a tooth, and a body extending from the base. An archwire slot extends across the body in a generally mesial-distal direction. A latch is connected to the body for releasably retaining an archwire in the archwire slot. The latch releases the archwire from the archwire slot in a certain direction whenever the archwire exerts a force in the range of about 0.1 kg to about 5 kg in the same direction on the appliance.
The present invention is directed in another embodiment toward an orthodontic appliance that comprises a base for bonding the appliance to a tooth and a body extending from the base. The appliance also includes an archwire slot that extends across the body in a generally mesial-distal direction. A latch is connected to the body for releasably retaining an archwire in the archwire slot. The latch releases the archwire from the archwire slot whenever the archwire exerts a force in a certain direction on the appliance that exceeds a certain minimum value. The minimum value is less than about one-half of the force required in the same direction to debond the appliance from the tooth.
Another embodiment of the invention is also directed toward an orthodontic appliance that comprises a base for bonding the appliance to a tooth and a body extending from the base. An archwire slot extends across the body in a generally mesial-distal direction and has an occlusal side, a gingival side and a lingual side. A channel extends in a generally occlusal-gingival direction along a path located lingually of the archwire slot. A latch is connected to the body for releasably retaining an archwire in the archwire slot. The latch is movable to a slot-open position to enable passage of the archwire into the slot by pressing the archwire against the latch in a direction toward the lingual side of the archwire slot. The latch includes a lingual portion that is received in the channel. The latch also includes a pair of arm portions that extend toward each other along a labial side of the archwire slot.
The present invention is also directed toward a method of releasing an archwire from an archwire slot of an orthodontic appliance. The method includes the act of placing at least one leg of a hand instrument along a tooth-facing side of the archwire. The method also includes the act of manipulating the hand instrument in order to urge the archwire in a direction toward a latch of the appliance. The method further includes the act of pressing the archwire against the latch with sufficient force to open the latch and release the archwire from the archwire slot.
These and other aspects of the invention are described in more detail below and are illustrated in the accompanying drawings.